The present invention relates to polyester resins, and more particularly to a two component sprayable polyester resin mixture, and most particularly to such a sprayable resin mixture incorporating a filler material that function as a fast curing surface sealer for porous surfaces.
Decorative honeycomb panels are employed as interior walls and partitions in aircraft and in other structures requiring lightweight but strong and rigid wall and partition members. The honeycomb panels comprise a honeycomb core onto which are laminated surface panels. The surface panels and the cores are usually composed of a phenolic/epoxy polymer or similar material. The exterior surface of the surface panels is usually quite porous and contains pinholes which must be filled prior to application of an exterior decorative lamina to the panels. In accordance with prior art techniques, a surface filler is employed to fill the pores and pinholes in the surface of the panels and is thereafter sanded to form a smooth, nonporous base layer onto which decorative coatings are laminated. One prior art surface filler includes a polyester resin and styrene monomer mixed with fillers such as talc or glass microballoons. Prior to application to the panels, the filled polyester resin is admixed with a promoter, such as dimethyl aniline, and a peroxide catalyst, such as methylethylketone peroxide or benzoyl peroxide. Since benzoyl peroxide in its pure form is a solid, it is normally admixed with a catalyst carrier, such as butylbenzyl phthalate, to form a catalyst paste. When the paste is added to the resin mixture, viscous resinous mass is formed which cannot be brushed or sprayed onto a surface. Once the catalyst paste is added to the filled polyester resin, the resin begins to cure almost immediately, requiring that the catalyzed resin mixture be applied to the honeycomb surface panels soon after mixing. Consequently, the resulting catalyzed resin mixture is normally applied with a spatula to the surface panel as soon as the catalyst is added to the resin. The resin mixture is then allowed to cure and is thereafter sanded to form a smooth, nonporous substrate onto which one or more decorative laminae can be applied.
Although the foregoing composition and application method are satisfactory to produce a sealed surface on honeycomb panels, they do have certain drawbacks. Since the catalyzed resin mixture is applied with a spatula, the resulting coating is relatively thick and also has a considerable variation in thickness. Further, hand application of the resin mixture is laborious and thus less efficient than is desired. Moreover, once the catalyst and resin are intermixed, the resulting mixture must be applied to the surface within a very short time. Thus, considerable time is periodically employed in mixing batches of resin for immediate application to surface panels, which time could otherwise be advantageously used to coat additional panels.
Accordingly, it is a broad object of the present invention to provide a surface sealer for honeycomb panels that has a long shelf life, that requires little or no mixing effort, and that is easy to apply in a relatively thin and even coating on a surface panel. It is a further object of the present invention to provide a fast curing, sprayable surface sealer for honeycomb surface panels, and more particularly to provide a fast curing, sprayable, polyester resin based surface sealer. Further objects of the present invention are to provide such a sprayable polyester composition that can be sprayed with relatively unsophisticated and inexpensive equipment and that will not tend to clog or plug the spray nozzles of the equipment. Most importantly, it is an object of the present invention to provide such a sprayable polyester resin surface sealer that cures sufficiently so that it can be sanded in on the order of from 30 to 45 minutes and that is easily sandable to a smooth, nonporous substrate onto which decorative laminae can be applied.